1. Field of the Invention
The present invention relates to a liquid crystal display device and, in particular, to a reflection type liquid crystal display device which effects display by using external light.
2. Description of the Related Art
Recently, the demand for longer operational life in portable information apparatuses such as notebook PCs and electronic notebooks when connected to a portable power supply (e.g. a battery) has increased. Mechanisms that lead to this longer operational life include an increase in battery capacity and a decrease in power consumption of the apparatus. The display in a portable information apparatus is one of the devices that uses a large amount of power. Thus, to lower the amount of power used, it is useful to decrease the amount of power consumed in displaying information to the user. For this reason, devices using liquid crystal displays (or liquid crystal display devices) are widely used as low power consumption displays. In general, conventional liquid crystal display devices use backlighting to aid in displaying data. However, the use of backlighting consumes power. Thus, a reflection type liquid crystal display device, which does not use a backlight is effective in achieving a reduction in power consumption.
As shown in FIG. 10, a conventional reflection type display device 100 comprises a pair of glass substrates 113 and 114, transparent electrode layers 120 and 121 respectfully provided on the opposing (inside) surfaces of the glass substrates 113 and 114, liquid crystal orientation films 122 and 123 respectively provided on the transparent electrode layers 120 and 121, and a liquid crystal layer 115 provided between the orientation films 122 and 123. First and second polarizing plates 117 and 118 are respectfully provided on the other surfaces (outside) of the glass substrates 113 and 114. A reflection plate 101 is provided on the outside of the second polarizing plate 118. The surface of a reflection film 105 on the reflection plate 101 is disposed between the reflection plate 101 and the second polarizing plate 118. Note that the terms inside (or inner side) and outside (or outer side) have been used here to denote sides of layers more proximate and more distal, respectfully, to the liquid crystal layer 115.
In the reflection type liquid crystal display device 100 described above, light impinging upon the first polarizing plate 117 undergoes linear polarization, and is further transmitted through the liquid crystal layer 115 to become elliptically polarized. The second polarizing plate 118 changes the elliptically polarized light into linearly polarized light, the reflection plate 101 reflects the linearly polarized light, which is subsequently transmitted through the second polarizing plate 118 and the liquid crystal layer 115 and emitted from the first polarizing plate 117.
In the conventional reflection type liquid crystal display device described above, the reflection plate 101 is endowed with scattering reflection characteristics by, for example, forming a reflection layer consisting of aluminum or the like on the rough surface of a metal film, synthetic paper or the like.
One problem with the typical reflection plate described above is that it has wide scattering angle characteristics, which is to say that it is difficult to enhance the brightness in a particular, frequently viewed direction (as in the case of the front of the display surface as viewed by the user). As a result, although the angle of sight is wide, the display is rather dark.
Alternatively, a flat, mirror-like surface may be used as the reflection surface rather than the rough reflection surface described above. When a mirror surface is used as the reflection surface, it is possible to obtain very bright characteristics in the specular direction with respect to the incident light. However, a disadvantage of using a mirror surface as the reflection surface is that when viewing the display from a direction that deviates slightly from the specular direction, the display is dark.
Thus, ideal reflection plate characteristics include both a wide viewing angle and high brightness. In view of this, effective scattering reflection in the viewing direction is desirable. A mechanism for achieving these characteristics is using a reflection plate having an intentionally controlled reflection scattering angle. It is also desirable for the arrangement to be random to avoid coloring due to the interference of the reflection light.
To control the reflection scattering angle, it may be possible to use machining or the like to form controlled, minute protrusions and recesses. However, when a completely random arrangement is adopted, the coordinate data on the work points is enormous and is impractical to create this type of reflection plate. Alternatively, it may be possible to generate random coordinates each time machining is conducted. In this case, however, it would be difficult to control the reflection scattering angle.
In addition, as a practical matter, it is easier from the viewpoint of designing and machining to form a random arrangement in a small-scale region and repeat the arrangement. In a possible example, recesses (or protrusions) are sequentially mechanically formed on the surface. It is convenient to form either one shape or a plurality of shapes at one time in a certain place on the surface and subsequently feed the surface sequentially in the X-direction in a fixed pitch, feed the machining position in the Y-direction after machining for a predetermined length, and perform surface processing while again feeding in the X-direction. This machining method results in a structure having a repeated arrangement in the machining feeding direction.
Using a reflection plate having a repeated arrangement (either formed by this or other methods) and combining with a stripe-shaped electrode as a display electrode may result in periodic overlapping between the patterns if the directions of the repeated structures do not completely coincide but are slightly angled with respect to each other. This periodical overlapping creates a fringe-like pattern, which is oblique with respect to the pattern direction, and results in a so-called moirxc3xa9 fringe being viewed. Even if a reflection type liquid crystal display device of this type is combined with color filters to perform color display, a moirxc3xa9 fringe is viewed due to the repeated structure of the protrusions and recesses of the reflection plate and the repeated alignment structure of the colored pixels of the color filters. The moirxc3xa9 fringe created impairs the display quality.
The present invention has been made with a view toward solving the above problem. It is an object of the present invention to provide a liquid crystal display device having a decreased viewable oblique moirxc3xa9 fringe while using a reflection plate having satisfactory reflection characteristics with a repeated recess arrangement and which is superior in display quality.
In accordance with the present invention, there is provided a reflection type liquid crystal display device comprising upper and lower substrates, a liquid crystal layer provided between the upper and lower substrates, a plurality of transparent electrodes formed on the side of at least one of the opposed surfaces of the upper and lower substrates so as to extend in a predetermined direction, and a reflection member on the opposed surface side or outside of the lower substrate, the reflection member having a plurality of recesses arranged in a direction, wherein the direction in which the recesses are arranged is deviated about 2.5 to about 40 degrees from the direction in which the transparent electrodes extend, thereby decreasing the viewable moirxc3xa9 fringe and improving the display quality of the liquid crystal display device.
Further, in accordance with the present invention, there is provided a reflection type liquid crystal display device, wherein the reflection member has on its surface a plurality of recesses the inner surfaces of which constitute part of spherical surfaces and which are formed continuously so as to overlap each other, the depth of the recesses and the pitch of adjacent recesses varying within predetermined ranges, whereby it is possible to obtain a bright reflection plate free from interference of light, thereby making it possible to improve the display quality of the liquid crystal display device.
Further, in accordance with the present invention, there is provided a reflection type liquid crystal display device which adopts an STN or TFT system wherein the reflection member is provided on the liquid crystal layer side of the lower substrate and wherein a polarizing plate is provided on the upper substrate.
Furthermore, in accordance with the present invention, there is provided a reflection type liquid crystal display device comprising a pair of substrates, a liquid crystal layer placed between the pair of substrates, a plurality of transparent electrodes formed in parallel at predetermined intervals on opposed surfaces of the pair of substrates, the opposed transparent electrodes being orthogonal to each other, and a reflection member provided on the side of one of the opposed surfaces of the substrates or on the outside, the reflection member having a plurality of recesses continuously formed so as to be arranged in two directions orthogonal to each other, the two directions in which the plurality of recesses are arranged are deviated by an angle of about 2.5 to about 40 degrees from the two directions in which the transparent electrodes orthogonal to each other extend.
In this reflection type display device, the moirxc3xa9 fringe interval is small, thereby decreasing the viewable moirxc3xa9 fringe and improving the display quality of a liquid crystal display device.
In the present invention, minute protrusions and recesses are formed on the surface of the reflection member, and the protrusions and recesses are repeatedly arranged according to a fixed regulation.
In the present invention, a preferable reflection member has a plurality of recesses continuously formed on the surface whose inner surface constitutes a part of a spherical surface, the depth of the recesses being in the range of 0.1 to 3 xcexcm, the inclination angle distribution of the recess inner surface being in the range of xe2x88x9235 degrees to +35 degrees, the pitch of adjacent recesses being in the range of 5 xcexcm to 50 xcexcm.
The xe2x80x9crecess depthxe2x80x9d is the distance from the surface of the reflection member to the bottom of the recess, and the xe2x80x9cpitch of the adjacent recessesxe2x80x9d is the distance between the centers of the recesses, which are circular in plan view. Further, the xe2x80x9cinclination angle of the recess inner surfacexe2x80x9d is the angle of the inclined surface with respect to the horizontal surface in the minute range when a minute range of 0.5 xcexcm width is taken at an arbitrary position on the inner surface of the recess 4. It is assumed that the angle of the reflection inclined surface of each recess with respect to a normal extending from the reflection member surface is positive and that the angle of the opposed inclined surface is negative.
In this preferable reflection member, it is important that the inclination angle distribution is set in the range of xe2x88x9235 degrees to +35 degrees and that the recess pitch is arranged random with respect to all directions of the plane. If there should be any regularity in pitch in adjacent recesses, the interference colors of light would appear, coloring the reflection light. If the inclination angle distribution of the recess inner surface is beyond the range of xe2x88x9235 degrees to +35 degrees, the inclination angle of the reflection light is too wide, and the reflection intensity deteriorates, making it impossible to obtain a bright reflection plate (The diffusion angle of the reflection light is over 70 degrees in the air, resulting in a reduction in the reflection intensity peak in the interior of the liquid crystal display device and an increase in total reflection loss.
Further, when the recess depth is more than 3 xcexcm, the vortex of the protrusion cannot be buried in the flattening film when flattening the recesses in the post process, making it impossible to achieve a desired flatness.
When the pitch of the adjacent recesses is less than 5 xcexcm, there is a limitation to the preparation of the mould for forming the reflection member, and a configuration which would provide desired reflection characteristics cannot be obtained, interference light, etc. being generated. In fact, when a diamond indenter having a diameter of 30 to 100 xcexcm that can be used for the preparation of the mould for forming the reflection member is used, it is desirable for the pitch of the adjacent recesses to be 5 to 50 xcexcm.
It is desirable for the pitch of stripe-like transparent electrodes arranged side by side to be 50 to 500 xcexcm. Further, it is desirable for each line width to be 40 to 490 xcexcm.
If the pitch of the transparent electrodes arranged side by side is less than 50 xcexcm, there is a limitation to the machining of the transparent electrodes; if it is more than 500 xcexcm, the pixels become rather large, making it impossible to obtain desired display characteristics and display quality.
Further, if the line width between the electrodes is less than 40 xcexcm, there is a limitation to the machining of the transparent electrodes; if it is more than 490 xcexcm, the pixels become large, making it impossible to obtain desired display characteristics and display quality.
In the reflection member, the two orthogonal directions in which a plurality of protrusions and recesses are arranged are deviated about 2.5 to about 40 degrees from the two directions in which the orthogonal electrodes extend since, if the deviation is less than about 2.5 degrees, moirxc3xa9 fringe that can be viewed will be generated and, if it is more than about 40 degrees, another moirxc3xa9 fringe that can be viewed will be generated.
Further, in accordance with the present invention, there is provided a reflection type liquid crystal display device comprising upper and lower substrates, a liquid crystal layer provided between the upper and lower substrates, a plurality of transparent electrodes formed on at least one opposed surface side of the upper and lower substrates so as to extend in a predetermined direction, a reflection member provided on the opposed surface side or outside of the lower substrate, and color filters provided on one of the opposed sides of the upper and lower substrates, the reflection member having a plurality of recesses arranged in a direction, wherein the direction in which the recesses are arranged is deviated about 2.5 to about 40 degrees from the direction in which a plurality of colored pixels of the color filters are aligned, thereby decreasing the viewable moirxc3xa9 fringe and improving the color display quality.
Further, in accordance with the present invention, there is provided a reflection type liquid crystal display device wherein the reflection member has a plurality of recesses the inner surfaces of which constitute part of spherical surfaces, the depth of the recesses and the pitch of the recesses varying within predetermined ranges, whereby it is possible to obtain a bright reflection plate free from interference of light, making it possible to achieve an improvement in color display quality.
Furthermore, in accordance with the present invention, there is provided a reflection type color liquid crystal display device which adopts an STN or TFT system wherein the reflection member is provided on the liquid crystal layer side of the lower substrate and wherein the color filters or overcoat layer is sequentially provided on the reflection member, a polarizing plate being arranged on the upper substrate.
Furthermore, in accordance with the present invention, there is provided a reflection type color liquid crystal display device comprising a pair of substrates, a liquid crystal layer placed between the pair of substrates, a plurality of transparent electrodes formed in parallel at predetermined intervals on opposed surfaces of the pair of substrates, the opposed transparent electrodes being orthogonal to each other, a reflection member provided on the side of one of the opposed surfaces of the substrates or on the outside, and color filters provided on the side of one of the opposed surfaces of the substrates, the reflection member having a plurality of recesses continuously formed so as to be arranged in two directions orthogonal to each other, the two directions in which the plurality of recesses are arranged are deviated by an angle of about 2.5 to about 40 degrees from the two directions in which the transparent electrodes orthogonal to each other extend, the two directions in which a plurality of colored pixels of the color filters are aligned are identical with the two directions in which the electrodes orthogonal to each other extend.
In this reflection type color liquid crystal display device, the moirxc3xa9 fringe can be reduced to such a degree that it is hard to view, and the reflection member provides a high reflection efficiency in all directions, so that, compared with the conventional reflection type color liquid crystal display device, it is possible to provide a reflection type color display device which is brighter and which has more satisfactory display quality.
As the above reflection member and electrodes, it is possible to use the reflection member and electrodes in the above-described reflection type liquid crystal display device.
In the color filters, it is desirable to arrange a plurality of colored pixels in parallel in rows at an inter-row pitch of 50 to 500 xcexcm, and the row width of each colored a pixel row is preferably 40 to 490 xcexcm. If the inter-row pitch of the colored pixel rows arranged in parallel is less than 50 xcexcm, there is a limitation to the processing of the colored pixel rows; if it is more than 500 xcexcm, the pixels become rather large, making it impossible to achieve desired display characteristics and display quality.
Further, if the row width of each colored pixel row is less than 40 xcexcm, there is a limitation to the processing of the colored pixel rows; if it is more than 490 xcexcm, the pixels become rather large, making it impossible to achieve desired display characteristics and display quality.